FACTSHEET April 2014

Dr Jason Smith Post-harvest care of grapevines: Charles Sturt University Irrigation and nutrition Dr Bruno Holzapfel NSW Department of Primary Industries

Temperatures in most Australian grape-growing Carbohydrate reserve storage and dynamics regions are warm enough for vines to retain their In spring, grapevines use carbohydrates from stored reserves in leaves for a period of time after harvest. In cooler perennial tissues to support new root and shoot growth. These areas, this may only be for a few weeks, but more carbohydrates are stored as starch and as free sugars, mainly glucose, fructose and sucrose. The combined concentrations of commonly it extends from 1 to 4 months in the starch and sugars in the roots range from approximately 3 to hotter, inland regions. 50% on a dry weight (DW) basis, and in the wood from 2 to 20% DW (Figure 1a). Starch is stored as granules within the xylem and Continued photosynthesis and nutrient uptake during the post- phloem ray cells, and areas of high starch concentrations can be harvest period allow vines to store carbohydrate and nutrient seen at the whole-tissue level after staining with iodine (Figure reserves for use in the next season. The aim of this factsheet is to 2). During the growing season, starch concentrations are higher describe the roles that carbohydrate and nutrient reserves play than those of sugar in the wood, but leading into dormancy some in the seasonal growth cycle of grapevines, and to discuss how starch is converted to sugar to help protect the vine from cold irrigation and fertiliser inputs can be used most efficiently to damage during winter. In roots, starch is the main form of storage promote carbohydrate and nutrient storage during the latter part carbohydrate all year round. of the season. The total amount of carbohydrate reserves stored by dormant grapevines ranges between 0.52 and 2.2 kg/vine, with a typical single-cordon vine storing between 50 and 75% of its total reserves in the root system. Research suggests that more than 80% of these reserves can be used if needed, but normally (a) less than half of the total stored carbohydrates are mobilised in spring. The difference provides vines with some buffering capacity to grow new shoots or leaves after events such as frost

(b)

Figure 1: Concentration ranges of carbohydrate reserves (a) and macronutrients N, P Figure 2: (a) Transmission electron microscopy image of starch granules (st) in a and K (b) in grapevine root, wood and cane tissue at dormancy. Figures based on a xylem ray cell of a dormant grapevine cane, and (b) a 2-year-old wood section at survey of 34 own-rooted and grafted Shiraz and Chardonnay blocks across southern dormancy, showing areas of high starch storage in the xylem rays after the starch NSW over three consecutive seasons (Smith et al. 2009; Smith, Quirk & Holzapfel granules have been stained blue with iodine. [Images courtesy Helen Waite (top), unpublished) Jason Smith (bottom)] 1

www.gwrdc.com.au Post-harvest care of grapevines: Irrigation and nutrition carbohydrate reserve concentration (%DW) reserve concentration carbohydrate Figure 3: Seasonal pattern of carbohydrate reserve dynamics in the wood and roots of mature own-rooted Shiraz vineyards at two locations during the 2006/07 season. Growth stage dates are shown for bud-break (BB), flowering (FL), veraison (V), harvest (HF) and leaf-fall (LF). The yield and pruning weight ratio were (a) 13 t/ha and 4.6 respectively for the Wagga Wagga vineyard, and (b) 6 t/ha and 2.2 for the Canberra vineyard (adapted from Holzapfel et al. 2010). or hail. Localised carbohydrate reserves are used to support high temperatures where photosynthesis is reduced may cause initial shoot growth. In the weeks after bud-break, carbohydrate reserve replenishment to be delayed. Under heavy crop loads, reserves from more distant parts of the vine are progressively mobilisation of carbohydrates may also occur in the earlier part of utilised as vascular connections develop between the new shoot the ripening period to aid berry ripening. In these situations, the and mature wood from the previous season. Transport of reserve post-harvest period is of particular importance for carbohydrate carbohydrates to the shoot reaches a maximum at the 8- to 10- storage and to ensure long-term vineyard productivity leaf stage, and then declines as canopy photosynthesis becomes sufficient to meet carbohydrate demand. Newly produced Nutrient reserves carbohydrates then start to be exported back to the perennial As early nutrient demand in spring cannot be met by root uptake parts of the vine. Below the ground, root growth flushes that alone, storage of nutrient reserves prior to dormancy is also occur in early spring are supplied from carbohydrates stored in required to support shoot growth in the following season. The the permanent roots. cycling of nutrients, and thus the vine’s ability to store them and remobilise them again in spring, depends on nutrient mobility within the plant. This is high for the macronutrients nitrogen (N), phosphorus (P), potassium (K), sulphur (S) and magnesium (Mg), but low for calcium (Ca). With the exception of manganese (Mn), which also has low mobility, the micronutrients iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo) and boron (B) have intermediate mobility.

Figure 4: Carbohydrate reserves are used to support initial shoot growth in grapevines The high initial dependence on stored carbohydrates leads to a decline of starch concentrations in root and wood tissue through bud-break and into early spring (Figure 3). In the week or two leading up to flowering, the canopy begins to produce sufficient carbohydrates to replenish wood and root reserves. These stores continue to build in parallel with fruit ripening, provided that yields are sufficiently low, or photosynthesis rates high enough to produce excess carbohydrates. However, under high crop loads, conditions of vine stress such as water deficit or Figure 5: Leaf senescence after harvest. The post-harvest period is a critical time for carbohydrate storage in grapevines 2

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Studies with whole mature vines have shown that about 50% of These observations would suggest that a fairly broad window N and P in the new season’s canopy comes from stored reserves. of opportunity for nutrient uptake exists from before flowering Around 15% of the demand for K is met by reserves, and 5% of to veraison in warm- to hot-climate vineyards. Post-harvest root that for Mg and Ca. Of the main macronutrient reserves, N is flushes are also observed, although these are generally smaller in stored in the highest concentrations, followed by K and P (Figure magnitude, and do not occur every year. In these vineyards, fine 1b). Average Mg concentrations in the roots and wood are roots can survive into winter, and may even continue to absorb similar to those of P, and Ca is found in approximately the same some nutrients after leaf-fall. concentration as K. There is little published information regarding the storage of micronutrients by grapevines. Impact of reserves on shoot growth and yield Total N storage at dormancy ranges from approximately 25 to High carbohydrate and nutrient reserves, and in particular stored 70 g/vine, and like carbohydrate reserves, more than half will N, will encourage strong spring shoot growth and promote usually be found in the root system. For P, which is the other higher bud fruitfulness. In research trials where carbohydrate main nutrient reserve (in terms of the proportion of total reserves reserves had been reduced by partial or complete defoliation, mobilised at bud-break), stored amounts range from 2.5 to reductions in shoot growth rates and diameters were observed 4.5 g/vine. For the other macronutrients, dormant vines store in the following spring (Bennett et al. 2005; Smith & Holzapfel 10–25 g of K, 4–8 g of Mg, and 25–40 g of Ca. In warm climates, 2009). Over successive seasons, reductions in shoot growth approximately one third of annual N and P requirements are caused by low reserves can also be accompanied by reduced met by post-harvest storage from the preceding season, 20% for bud fertility and lower flower numbers on bunch inflorescences Mg and Ca, and 15% for K. Storage of nutrients during the post- (Figure 6). The subsequent processes of flowering and fruit-set harvest period is due to both re-translocation from the leaves, are also influenced by carbohydrates, but the supply from current particularly for N and P, and further root uptake from the soil. photosynthesis is more important than that from stored reserves (Rogiers et al. 2011). Grapevine root growth style Fine roots are important for the uptake of nutrients and water (Figure 5), and the peak of fine root growth can generally be expected between flowering and veraison in Mediterranean and cool temperate climates (Comas et al. 2010). In hot irrigated regions of Australia (e.g. the Murray Darling Basin), recent studies indicate that fine root growth can commence at or before bud- break in some seasons, with new roots present to some extent from spring through to mid-summer (EJ Edwards, personal communication; Smith & Holzapfel, unpublished data).

Figure 6: Numbers of flowers on bunch inflorescences can be negatively affected by low grapevine carbohydrate reserves

There is evidence that N reserves play a greater role than carbohydrates in regulating shoot growth after bud-break, but the effects of the two can be difficult to separate. However, grapevines will use stored N to support initial shoot growth irrespective of soil N availability, and then transition to new- season uptake in the weeks leading up to flowering. The N status of the vine at the end of the post-harvest period will therefore have an important impact on the development of the canopy in the following spring. Figure 5: Soil pit excavation showing fine roots (painted white) within soil profile, which are critical for nutrient and water uptake 3

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Post-harvest vine management: Carbohydrate storage For carbohydrate storage to occur after harvest, continued photosynthesis is required. This means maintaining the leaves in reasonable condition for as long as possible after harvest with adequate irrigation and nutrition. Effective pest and disease control through the season is also important to ensure a healthy canopy. Apart from the loss of functional leaf area, infections with powdery or downy mildew can considerably disrupt and reduce carbohydrate export from the leaves. (See www.gwrdc.com.au/ resource_categories/pest-and-disease for more information.) The carbohydrate status of vines at harvest is most influenced by seasonal weather conditions, yield and harvest date. In cooler climates, vine carbohydrate reserves are largely restored by harvest (Figure 7). Late-season defoliation may still have an impact on carbohydrate reserve accumulation, but this needs to occur across several consecutive seasons before effects on growth and yield are observed (Greven et al. 2012). Figure 8: Vine canopies in poor condition may not have enough capacity to ripen fruit and store reserves at the same time

A direct measurement of carbohydrate reserve status at harvest provides the most definitive method for assessing the importance of the post-harvest period. However, a general guide to the need for post-harvest replenishment can be obtained from the vine yield. Slow or uneven berry ripening and delayed or incomplete cane lignification can provide additional indicators that vines have experienced a shortage of carbohydrates during the season. With lower-yielding vines up to about 10 t/ ha, sufficient carbohydrates will usually be stored in parallel with fruit ripening if growing conditions have been favourable. Post-harvest reserve storage becomes more important as yields increase from 10 to 20 t/ha, but other than maintaining some irrigation if rainfall is low through late summer and early autumn, little management intervention is required. However, for fruit yields from 20 to 30 t/ha and above, the post-harvest period becomes increasingly critical for sustaining long-term vine productivity and some 6–8 weeks may be required for full restoration of reserves. In these situations, it is important that irrigation is used to maintain leaf photosynthesis after harvest,

Figure 7: Grapes just before harvest. Vine carbohydrate reserves are largely restored and for early harvest dates in particular, that leaf and canopy by harvest in cool climates but in hot climates there is a greater reliance on the function are retained through any remaining summer heat post-harvest period for replenishment of reserves events. In hot irrigated regions, at the other end of the climate spectrum, Post-harvest vine management: yields are typically higher and temperatures during the ripening period are often in the optimal range for photosynthesis. If vines Nutrition are water-stressed during these periods or suffer significant heat For the overall management of grapevine nutrition, using damage to the leaves, the canopy may not have the capacity to combinations of annual petiole test results, knowledge of soil ripen fruit and store reserves at the same time (Figure 8). In these conditions, visual canopy assessments and juice N concentrations situations, the vine has a greater reliance on the post-harvest (if available) is currently the best way to assess vineyard nutrient period for reserve replenishment. The loss of leaf area following status. Nutrient removal rates with fruit can also be considered machine harvesting can impact on reserve storage, but provided (Nicholas 2004). Post-harvest fertiliser applications provide an this doesn’t exceed 40–50% and the remaining leaves remain opportunity to address any late-season nutrition issues, promote healthy, the effects will be minimal. the retention of leaves for a longer period into autumn, and build 4

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up nutrient reserves for the following season. However, nutrition with sometimes very limited water availability though to strategies may vary between regions, and according to the time intermediate-yielding vineyards with reliable water supplies. available for mobile nutrients such as N to move into the root- Where canopies have suffered leaf damage or water stress during zone and be taken up by the vine before leaf-fall. the ripening period, N applications with irrigation shortly after Hot-climate irrigated vineyards harvest can assist with maintaining leaf function into the post- harvest period. The majority of growers in hot-climate irrigated regions apply fertiliser during the post-harvest period, with N, P and K the most commonly applied nutrients. Post-harvest N applications in particular can assist with maintaining functional leaf area for a longer period after harvest, and given the role of stored N in supporting spring shoot growth, it is also important that N reserves are replenished in the post-harvest period. Of the other main macronutrients, P and K may also be taken up in the post- harvest period, but as these have much lower mobility in the soil, timing of application is less critical than for N.

Figure 10: Vineyard following harvest with obvious leaf senescence

Even for low-yielding vineyards, storage of N reserves will also occur in the post-harvest period. In situations where irrigation water is limited and chances of post-harvest rainfall low, there will be limited movement of nutrients into the rootzone. Any fertiliser applications should be delayed until the next season to avoid leaching losses over winter.

Cooler-climate management As the duration of the post-harvest period decreases, the Figure 9: Early season application of nitrogen may be beneficial for vines with known deficiencies scope for varying management practices during this time also decreases. With a short post-harvest period, there may only be The amount and type of fertiliser applied after harvest needs the opportunity (or need) for one or two irrigations timed with a to take into account the overall nutritional status of the vines. fertiliser application before leaf-fall. For locations where leaf-fall For N, which is the most important nutrient to consider for the normally occurs shortly after harvest, vine nutrition by default is post-harvest period, about one quarter to a third of the total managed with fertiliser applications earlier in the season. Soil or seasonal requirement might typically be applied in this period. If, foliar N applications around veraison will primarily be directed to at harvest, vines have a canopy in good condition and no major the fruit, but applications closer to harvest may be effective for indications of N deficiency, fertiliser applications may be able to increasing leaf and reserve N later in the season. wait until early autumn. Alternatively, earlier applications may be beneficial for vines with known marginal N concentrations (Figure 9). In both cases, Post-harvest vine management: irrigation should be managed to minimise water movement and Irrigation loss of soluble N forms below the rootzone. Where possible, some water should be saved for use during the post-harvest period. This allows for some irrigation to maintain Warm-climate vineyards leaf function, and in the absence of rainfall, to help move any applied fertilisers into the rootzone. In the event that no water is Warm-climate viticultural regions in Australia represent a available for irrigation during the post-harvest period, research diverse array of growing conditions, from low-yielding vineyards suggests that even high-yielding vines can tolerate this for one

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or two seasons. Carbohydrate reserve accumulation in the roots Acknowledgements may be reduced, but provided that vines have had reasonable irrigation or rainfall prior to harvest, the amount of reserves The authors would like to acknowledge the contributions of Leo stored should still be adequate. However, if dry post-harvest Quirk and Stewart Field to the first version of this factsheet, which conditions are anticipated, it is advisable to save some water was prepared for the Water and Vine presentations in 2008. for an irrigation at the end of the season to avoid entering vine dormancy with a dry soil profile. An irrigation to bring the References and further reading main part of the rootzone back into the readily available water range in late winter, or several weeks before bud-break, may Bennett J, Jarvis P, Creasy GL & Trought MCT (2005) Influence of also suffice and will also assist in leaching applied salts from the defoliation on overwintering carbohydrate reserves, return bloom, rootzone. Vines that reach bud-break with a dry soil profile can and yield of mature Chardonnay grapevines. American Journal of have uneven and reduced shoot growth, possibly as a result of Enology and Viticulture 56(4): 386–393. a decline in root function and delay in vine rehydration (Keller Comas LH, Bauerle TL & Eissenstat DM (2010) Biological and 2010). Trials have also shown delays in ripening due to increased environmental factors controlling root dynamics and function: effects crop load, as dry soils through bud-break appear to have a of root ageing and soil moisture. Australian Journal of Grape and greater effect on canopy growth than yield (Holzapfel & Smith Wine Research 16: 131–137 (http://dx.doi.org/doi:10.1111/j.1755- 2012). 0238.2009.00078.x).

Greven MM, Neal SM, Tustin DS, Vasconcelos MC & Boldingh H (2012) The effect of postharvest defoliation on Marlborough Sauvignon Blanc productivity. NZ Winegrower Oct/Nov 74–77.

GWRDC (2009) Management of carbohydrate reserve accumulation as a tool for regulating vine productivity and fruit quality. Final Report for Project CSU 05/01. 83 pp. Available at www.gwrdc.com.au/wp- content/uploads/2012/09/CSU-05-01.pdf

Holzapfel BP & Smith JP (2012) Developmental stage and climatic factors impact more on carbohydrate reserve dynamics of Shiraz than cultural practice. American Journal of Enology and Viticulture 63(3): 333–342. (http://dx.doi.org/doi:10.5344/ajev.2012.11071)

Holzapfel BP, Smith JP, Field SK & Hardie WJ (2010) Dynamics of carbohydrate reserves in cultivated grapevines. In Janick J (ed.) Horticultural Reviews, vol. 37, John Wiley & Sons: Hoboken, NJ, pp. 143–201 (http://dx.doi.org/doi:10.1002/9780470543672.ch3).

Keller M (2010) The Science of Grapevines: Anatomy and Physiology, Academic Press: Burlington, MA, ISBN 9780123748812, 378 pp.

Nicholas P (2004) Soil, Irrigation and Nutrition, Grape Production Series, no. 2, Winetitles: Adelaide, ISBN 9781875130405, 201 pp.

Rogiers SY, Smith JP, Holzapfel BP & Hardie WJ (2011) Soil temperature Figure 11: In dry soils, irrigation prior to bud-break can avoid uneven and reduced moderates grapevine carbohydrate reserves after bud break and early season shoot growth conditions fruit set responses to photoassimilatory stress. Functional Plant Biology. 38(11): 899–909 (http://dx.doi.org/10.1071/FP10240).

Smith JP & Holzapfel BP (2009) Cumulative responses of Semillon grapevines to late season perturbation of carbohydrate reserve status. American Journal of Enology and Viticulture 60(4): 461–470.

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